a modified starch YS of heat tolerance up to 180℃was synthesized by using starch and a novel vinyl monomer containing sulfonic groups and quaternary aminonium cation ，as raw materials ，and the performance of fluid loss，salt and calcium resistance ，heat tolerance and inhibition were also evaluated. The experimental results showed that YS had better filtration reduction properties ，whatever in fresh water，seawater ，saturated brine，complex brine and calcium chloride brine base slurry. The filtrate loss of the drilling fluids could be controlled within 10mL after adding 1.5%-2.5% YS. The salt tolerance and anti-calcium performance were all to saturation，and the effect of filtration reduction and ability to improve viscosity and shear of the YS was enhanced with the increase of salt content. After adding 2.0% YS into the fresh water base slurry，the rising rate of apparent viscosity could decrease from 300% to73.3% ，while compared with the water，the 2.0% YS solution could make the linear expansion rate reduce from51.5% to 10.2% ，which indicated that YS had better performance in inhibiting hydration and expansion of shale.